Rheostat



M..L. NORRIS Sept. 10, 1929.

RHEOSTAT Filed March 51, 1926 Inventor Marvin L. Norris H a Q His Attorneu Patented Sept. 10, 1929.

UNITED STATES PATENT OFFICE.

MARVIN L. NORRIS, OF FORT WAYNE, INDIANA, ASSIGNOR T GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

RHEOSTAT.

This invention relates to rheostats and the improvements provided thereby are especially advantageous in small enclosedrheostats of the foot-operated typebrdinarily used for controlling sewing machine motors or in other similar service.

Among the advantageous features afiorded by the present invention are an improved form of controlling contact mechanism for inserting and removing portions of the regulating resistance from the controlled circuit, an improved arrangement of the casing within which the contact mechanism and the regulating resistance are enclosed, as well as an improved foot-operating means for the rheostat. Other advantageous features will be apparent from the following description of the accompanying drawing which illustrates a preferred form of foot-operated rheostat suitable for controlling sewing machine motors or other similar light duty service.

In the drawing, Fig. 1 is a perspective view showing the general form of the footoperated rheostat; Figs. 2, 3 and 4 are respectively a longitudinal sectional view, a transverse sectional view and a plan sectional view showing the details of construction of the rheostat; and Figs. 5 and 6 are sectional views showing the relation of the several parts of the rheostat during different phases of operation.

Referring to- Fig. 1, the regulating resistance element and the controlling contact mechanism therefor are enclosed within a casing or base 10 having a hinged cover 11 pivotally mounted upon the shaft 12 and adapted to telescope with the base 10 when pressure is applied to the operating stirrup 13 by the foot of an operator, as indicated in dotted lines. The operating stirrup 13 is pivotally mounted upon the free end of the cover 11 so as to swing forward when the cover 11 is depressed and in this way effectively eliminate the tendency of the rheostat to slide away from the operator.

As shown in detail in Figs. 2 and 3 the regulating resistance element 14 is formed 0 of suitable material such for example as carbon, graphite, or the like, in a rectangular shape, although any other suitable resistance element may be employed. However,.the form of resistance element shown is well adapted to successfully withstand severe shocks and jars as well as excessive heating and, furthermore, at little increased cost may be provided with a plurality of contacts 15, 16, l7, l8, l9, and 20, which are embedded in spaced alignment in the resistance element 14, as shown in broken section in Fig. 3 during the process of moulding or otherwise forming the resistance element. The'resistance element 14 is mounted in the case 10 by means of the sets of lugs 21 and 22 which are punched out of opposite sides of the base 10 to receive the resistance element 14 with the spacers 23 and 24 of suitable insulating material, such as asbestos or the like, between the resistance element'and the casing. The clamp 25 which also is suitably insulated from the resistance element firmly holds the resistance element in position.

In order to control the resistance element 14 the bridging member 26 is firmly secured to and insulated from the telescoping cover 1 and is provided with a plurality of resilient fingers 27, 28, 29, 30, 31 and 32, for successively engaging the contacts 15 to 20. The rivet-s 33 serve to secure the bridging member 26 to the cover 11 and as shown more in detail in Fig. 4 the insulating spacer 34 is interposedbetween the bridging mem' ber 26 and the cover- Also the bridging member 26 is provided with enlarged openings through which the rivets 33 pass and is held in fixed spaced relation therewith by the lugs 35 on the opposite sides of the bridging members, as well as the lug 36 on one edge of the bridging member, all of which register with suitable notches or slots formed in the strip of insulating material 37, which in turn is held securely by the IlVOtS 33.

To insure that the several resilient fingers of the bridging strip 26 are maintained in proper oblique aligment with the cooperating contacts on the resistance element so as to successively engage therewith, a support contacts on the resistance element and alsov to serve the further purpose of imparting an initial strain to the flexible yielding fingers of the bridging member. This permits the pressure with which each of the fingers of the bridging member engages with the corresponding contact of the resistance element to be regulated to a suitable value such that a firm conducting contact is established at thev moment of contact. In this way injurious arcing between the lingers and the contacts due to light contact pressure is effectively avoided.

The rheostat is connected in the circuit to be controlled by means of the twoconductor lead which has one conductor connected to the contact 20 on the resistance element and the other conductor connected to the lug 36 of the bridging member 26 as clearly shown in Figs. 2, 3, 4, 5 and 61 Thus when foot pressure is applied to the operating stirrup 13 so as to telescope the cover 1 11 with the base 10, the finger 27 first engages with the corresponding contact 15 and completes the circuit including all sections of the resistance element 14 and the current is maintained at 'minimum value, Upon further depressing the operating stirrup 13, the fingers 28, 29, 30, and 31 of the bridging member are brought into successive engagement with the corresponding contacts 16, 17, 18 and 19 to successively remove portions of the resistance element 14 from the controlled circuit until all of the resistance element is removed from the circuit by the engagement of the finger 32 with contact 20. During this process the stirrup 13 swings about its pivotal mounting on the cover 11 through the successive positions in which it is shown in Figs. 2, 5 and 6. As previously pointed out, this arrangement of the operat-iug stirrup overcomes the tendency of the rhcostat to slide out from under the foot of the operator and in this way facilitates operation of the rheostatand insures certainty in the control of the resistance element.

With the cover 11 fully telescoped as shown in Fig. 6 all of the resilient fingers of the bridging member 26 are in firm engagement with the corresponding contacts out of engagement with the fingersof the.

support 38. Upon the removal of pressure from the operating stirrup 13 the cover 11 is returned to its initial position by the biasing spring 41 which may be wound spirally about the pivot shaft 12 with one end extending into engagement with the base and the other into engagement with the cover as shown. The operating stirrup 13 is provided with an inwardly projecting stop 42 which is arranged to engage with the extension 43 from the base 10 so as to limit the upward movement of the cover 11. The stop 42 also permits the biasing spring 41 to return the operating stirrup 13 to its initial position as shown in Fig. 2.

The hinged cover 11 of the rheostat preferably is provided with suitable ventilating slots 44 to expedite the cooling of the resistance element 14. Also as shown in Figs. 2, 5 and 6, the base 10 is provided with the feet 45 and 46, the former preferably being drawn or punched out of the metal forming the casing 10, while the latter is of resilient adhesive material such as rubberto more effectively prevent slipping and sliding of the foot-operated rheostat. As may be seen from the drawing the foot 46 is formed of rubber in the general shape of an annulus having a central groove of restricted peripheral diameter adapted to fit securely in the opening 47 in the casing 10. In this way the two enlarged portions or rings 48, which are joined together by the cylindrical web 49 of reduced peripheral diameter to form the centralgroove, extend over and securely engage with the opposite sides of the casing 10 and thereby serve to firmly secure the foot 46 in the opening 47. To insert the foot in the opening in the casing, it is only necessary to compress one of the enlarged resilient rings 48 suficiently to pass through the opening whereupon the ring again expands and securely holds the foot in position.

From the foregoing it is thought that the ease of operation, the certainty of control, the sturdiness of construction and the consequent reliability in service of a rheostat embodying the improvements of my present invention, as well as the reduced cost of manufacture thereof, will be apparent to those skilled in the art.

WVhat I claim as new and desire to secure by Letters Patent of the United States, is:

1. A rheostat comprising a resistance element, means for controlling the same including a plurality of contacts and a cooperating bridging member having a plurality of resilient yielding fingers for successive ly engaging said contacts, and independently adjustable means for imparting an initial strain to each of said fingers so as to regulate the pressure exerted by the fingers upon engagement with the corre sponding contacts.

2. A rheostat comprising a resistance element, means for controlling the same including a plurality of contacts and a cooperating bridging member having a series of resilient yielding fingers for engaging said contacts, and a support for normally holding the resilient fingers .at unequal distances from the cooperating contacts to thereby cause the fingers to successively engage the contacts and for imparting an initial strain to each of said fingers to regulate the initial pressure exerted thereby upon the corresponding contact.

3. A rheostat comprising a resistance element, a plurality of contacts disposed in spaced alignment-and electrically connected .to different portions of said resistance element, a movable bridging member having a series of resilient yielding fingers for engaging said contacts, and a support secured to saidbridging member and having a plurality of adjustable fingers engaging with said bridging fingers for normally holding the resilient fingers in oblique alignment with the contacts to effect successive engagement therebetween upon move ment of the bridging member and for imparting an initial strain in eachof said fingers to thereby regulate the pressure with which each finger engages with the corresponding contact.

4;. An enclosed rheostat comprising a resistance element mounted in an enclosing casing having a telescoping cover, a plural- 1ty of contacts mounted in spaced alignment along said resistance, and a movable bridging member mounted on the cover; and having a series of resilient fingers arranged to be actuated into successive abutting engagement with said contacts and arrested thereby as the cover is telescoped with the casing. 4

5. An enclosed rheostat comprising a resistance element mounted in an enclosing casing having a telescopic cover, a plurality of contacts mounted in spaced alignment on said resistance, a movable bridging member mounted uponsaid cover and having a series of resilient yielding fingers engaging said contacts when the cover is telescoped with the casing, and a support secured'to said cover for holding the resilient fingers at unequal distances from the cooperating contact to efiect successive engagement therebetween.

6. A foot-operated rheostat comprising a resistance element, control contact mechanism therefor, a base for the rheostat, a member movable relative to the base for actuating said control contact mechanism, and a stirrup pivotally mounted upon said member for operatingthe same.

7. A foot-operated rheostat having two members hingedly connected for relative movement thereof, the first of said members being arranged to remain stationary and the second of said members being arranged to move With reference to the first about the hinged connection therebetween, a resist-' ance element mounted upon one of said members, a cont-r01 contact mechanism for the resistance element mounted upon the other of said members, and an operating stirrup pivotally mounted upon the freeend of said second member for operating the same.

8. A foot-operated enclosed rheostat comprising a resistance element mounted in an enclosing base having ahinged cover adapted to telescope therewith, control contact mechanismfor the said resistance element con: nected to be operated upon the telescoping of the cover with the base, and an operating stirrup pivotally mounted upon the free end of said cover for telescoping the same with said base.

9. A foot-operated enclosed rheostat comprising a resistance element mounted in an enclosing base having a hinged cover adapted to telescope therewith, a plurality of contacts mounted in spaced alignment upon said resistance element, a cooperating bridging member secured to said cover and having a plurality of resilient fingers disposed in oblique alignment with said contacts to successively engage the same upon the telescoping of the cover with the base, and an operating stirrup pivotally mounted upon the free end of said cover for telescoping the same with said base.

10. A foot-operated rheostat comprising two members hingedly connected for relative movement therebetween, the first of said members being arranged to remain stationary and the second of said members being arranged to move about the hinged connection therebetween, a resistance element mounted upon one of said members, a control contact mechanism therefor mounted upon the other of said members, an operating stirrup pivotally mounted upon the free end of said second member for operating the same, and a common means for biasing said members apart and for biasing said operating stirrup to a predetermined operating position.

11. A foot-operated enclosed rheostat comprising a resistance element mounted in an enclosing base having a hinged cover adapted to telescope therewith, a plurality of contacts mounted in spaced alignment on said element, a cooperating bridging member secured to said cover and having a plurality of resilient fingers for successively engaging said contacts, a stirrup pivotally mounted on the free end of said cover for telescoping the same with said base, and a common means for biasing said cover out of telescoping re lution with the base and said stirrup to a predetermined operating position.

In Witness whereof, I have hereunto set a my hand this 29th day of March, 1926.

MARVIN L. NORRIS. 

